Rotary cutting dies

ABSTRACT

A pair of rotary die cylinders with lands having coacting cutting edges which cut blanks from a web of material passing through the nip of the rotating dies. In cross section each land has an outer face and a pair of spaced apart side faces which are parallel to each other and perpendicular to the chord of the outer face to provide a clean cut and facilitate release of the cut blank from the cutting blades as it emerges from the nip of the dies. The die cylinders are journalled for rotation by recesses with frusto conical locating surfaces in their opposed ends. Each die cylinder is made by machining the recesses in the opposed ends of a generally cylindrical workpiece of tool steel and then utilizing the recesses to locate and orient the workpiece relative to a cutting tool to produce a cylindrical surface on the workpiece concentric with the axis of the recesses and then to machine away portions of the periphery of the cylindrical surface to form the cutting blade lands thereon. After machining is completed the cutting blade lands may be hardened by heat treating utilizing a laser beam directed onto the lands to heat them at an elevated temperature so that upon quenching they are hardened without any substantial hardening and resulting distortion of the core or body of the workpiece.

REFERENCE TO A APPLICATION

This is a continuation-in-part of U.S. patent application Ser. No.08/002,660 filed on Jan. 11, 1993, now abandoned, the disclosure ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to rotary die cutting of blanks from thin sheetsor webs of material, and more particularly to improved rotary cuttingdies and a method of making them.

BACKGROUND OF THE INVENTION

For many years, a pair of superimposed rotary dies with cutting bladeson one of both cylinders have been used to cut blanks from a thin web ofmaterial passing through the nip of the dies. Typically, the thin web isof a material such as paper, paper board, cardboard, plastic film, metalfoil, thin sheet metal and the like.

U.S. Pat. No. 4,608,895 discloses a pair of rotary die cylinders withintegral complementary cutting blades thereon which coact to sever a webof material passing through their nip. Each severing blade has anelongate land projecting generally radially outwardly from its cylinderand having in cross section an outer face and spaced apart dependingside faces inclined towards each other at an acute included angle, andeach inclined to its associated outer face at an obtuse included angle.When the line of severance subtends more than a quandrant, the cuttingedge transfers from one side edge to the other of the coacting lands ata pair of cross over sections each having an outer face which issubstantially narrower than the outer face of the adjacent portion ofthe land. To enable proper registration of the coacting lands to cut aweb, the pair of die cylinders can be relatively shifted both axiallyand in rotational phase with respect to each other.

The die is made from a cylindrical blank of tool steel which is hardenedand ground to produce a cylindrical surface before it is electricaldischarge machined (EDM) to produce the lands with the desired geometrythereon. To produce the desired accuracy and geometry of the lands, theyare EDM machined in the hardened cylindrical workpiece utilizing anegative electrode, which is preferably cylindrical with groovesmachined in the periphery thereof with a generally V-shape cross sectionfor forming the lands of the die cylinders.

While these die cylinders have been sold commercially and performedsatisfactorily for relatively high volume mass production operations,they are expensive and difficult both to manufacture and resharpen whenthey become worn or dull in use.

SUMMARY OF THE INVENTION

A pair of rotary die cylinders having coacting severing blades formed byintegral lands projecting generally radially outwardly from the mainbody of each cylinder and having in cross section, an outer face and apair of spaced apart side faces at least one and preferably both ofwhich are essentially perpendicular to the outer face or its chord. Aperpendicular side face and the outer face intersect to define a cuttingedge on the land, and preferably the other edge is chamfered. Tofacilitate disengaging the cut blank from the dies, preferably eachcoacting pair of cutting lands has an associated elongate ejector landlocated adjacent to them and within the perimeter of the line ofseverance of the cut blank. The ejector land is integral with the diecylinder having the cutting land disposed outside the cut blank andcooperates with the other cutting land (inside the cut blank) to flexthe blank.

The rotary die cylinder is made by machining in the opposed ends of atool steel workpiece, which is preferably generally cylindrical, a pairof recesses each having a bore with a frusto conical locator surfacetapering inwardly with both the of the bores lying essentially on thesame common axis of rotation. The tapered bores are used to accuratelylocate the workpiece while machining a peripheral cylindrical surface onit which is concentric with the common axis of rotation. Utilizing therecesses and frusto conical surfaces, the workpiece is located andoriented relative to a cutting tool to machine away material from theperiphery of the workpiece to form the cutting blade lands and anyejector lands. Subsequently, the machined cutting lands are hardened byheat treating utilizing the tapered bores to locate and orient themachined workpiece relative to a laser to direct its beam ofelectromagnetic energy onto the cutting blade lands to heat them to anelevated temperature from which they are cooled to harden them withoutsubstantially hardening the main body of the cylinder.

Objects, features and advantages of this invention are to provide a pairof rotary die cylinders with coacting cutting blades thereon which havea substantially longer useful life in service, require a substantiallylower cutting force requiring less power to drive the cylinders andproduce less load thereon, substantially reduce the likelihood of cutblanks being caught, trapped or hung up in the die cylinders, havingcutting blades which are easier, faster and more economical to resharpenafter becoming dull in use, a substantially longer in service usefullife, and rotary die cylinders and a method of making them which aresignificantly less expensive, may be made by machining with conventionalcutting tools, enable the cutting blades to be hardened after beingformed, and are relatively quick, easy, inexpensive and requires lesscapital investment to make them.

BRIEF DESCRIPTION OF THE DRAWINGS

These, and other objects, features and advantages of this invention willbe apparent from the appended claims, detailed description of the bestmode, and accompanying drawings in which:

FIG. 1 is a perspective view of a pair of cutting die cylindersembodying this invention for cutting blanks from a web passing throughtheir nip;

FIG. 2 is a fragmentary sectional view taken generally on line 2--2 ofFIG. 1 of a cutting blade land of the upper die;

FIG. 3 is a fragmentary sectional view of a modified form of a cuttingblade land of the die cylinders;

FIG. 4 is a semi-schematic sectional view taken in the plane of the axesof the die cylinders and illustrating flexing of the cut blank byejector lands of the die cylinders;

FIG. 5 is a fragmentary sectional view similar to FIG. 4 illustratingejector lands and the cutting blade lands after they have beenresharpened;

FIG. 6 is a semi-schematic side view illustrating the cutting off andmachining of the ends of a piece of tool steel bar stock to form agenerally cylindrical workpiece from which a die cylinder is made inaccordance with the process of this invention;

FIG. 7 is a semi-schematic side view illustrating the machining ofrecesses with tapered bores having frusto conical locator surfaces inthe opposed ends of the workpiece;

FIG. 8 is a semi-schematic side view illustrating the machining ofkeyways in the recesses of the workpiece;

FIG. 9 is a semi-schematic side view illustrating the machining of acylindrical peripheral surface on the workpiece concentric with thecommon axis of the tapered bore conical locator surfaces;

FIG. 10 is a semi-schematic side view illustrating machining of aportion of the periphery of the workpiece to form a cutting blade landthereon;

FIG. 11 is an semi-schematic and enlarged sectional view of theworkpiece illustrating the orientation of cutting tools for removingmaterial from the workpiece to form an axially extending land portion ofthe cutting blade thereon;

FIG. 12 is an enlarged and fragmentary cross sectional view of theaxially extending land portion of the cutting blade of FIG. 11; and

FIG. 13 is a semi-schematic side view of a laser directingelectromagnetic energy onto a machined cutting blade of the steelworkpiece to heat it to an elevated temperature for hardening or heattreating the cutting blade without hardening the core or main body ofthe workpiece.

DETAILED DESCRIPTION

Referring in more detail to the drawings, FIG. 1 illustrates a pair ofcutting die cylinders 20 and 22 embodying this invention with coactingcutting blades 24 and 26 thereon which when the cylinders areco-rotating cut generally rectangular blanks 30 from a web 32 of thinmaterial, such as paper board, passing through the nip 34 of the diecylinders. Preferably, removal of blanks from the die cylinders isfacilitated by pairs of ejector lands 36, 38 and 40, 42 within theperimeter of the cutting blades.

In use, each die cylinder is journalled for rotation by a pair of arborassemblies having coaxial spindles with opposed noses (not shown),received in complementary recesses 44 in the opposed ends 46 and 48 ofeach die cylinder. Each recess is a bore with a frusto conical sidewall50 tapered inwardly from its associated cylinder end which provides alocator surface engagable with a complementary tapered surface on thenose of an associated spindle. For each die cylinder, the frusto conicalsurfaces of both of its recesses are on the same or common axis ofrotation 52 or 54 of the cylinder. In use, each cylinder is driventhrough one or both spindles of its arbor assembly to co-rotate inopposite directions of rotation (counterclockwise and clockwise asindicated by the arrows in FIG. 1) with essentially the same peripheralsurface speed of its cutting blades. One or both spindles are alsocoupled to their associated cylinder for rotation therewith by a keyreceived in a keyway 56 in the recess of the cylinder. The constructionand arrangement of the recesses, keyways and frusto conical surfaces forjournalling, locating and driving the die cylinders 20 & 22 is disclosedin greater detail in pending U.S. patent application Ser. No. 08/002,660filed on Jan. 11, 1993, the disclosure of which is incorporated hereinby reference and hence will not be described in further detail.

To produce a clean cut, the dies are constructed so that the position ofthe cutting edges of the coacting blades 24 and 26 can be varied andadjusted by moving the dies axially and/or in rotary phase relationshipwith respect to each other. This is accomplished by locating variousportions of the cutting edge of the blade and its cutting edge of eachdie so that relative movement of the dies in one axial direction and/orone rotary phase direction causes all the cutting edges of the blades ofboth dies to move toward and even overlap each other and movement in theopposite direction causes all the cutting edges of all the blades ofboth dies to move away from and even be spaced from each other.

If the predetermined line of severance to be cut by the dies subtendsmore than one quadrant, it is necessary to locate the cutting edge onopposite sides of the blade along different longitudinal portions of theblade. For example, to cut the rectangular blank 30, the blade 24 of theupper die has circumferentially and axially extending land portions 58and 60 with inner cutting edges 62 and 64 and circumferential and axialland portions 66 and 68 with outer cutting edges 70 and 72 whichrespectively coact with the lower cylinder blade 28 circumferential andaxial lands 74 and 76 with outer cutting edges 78 and 80, andcircumferential and axial lands 82 and 84 with inner cutting edges 86and 88. With this arrangement, axial movement of the upper die cylinder20 to the left, as viewed in FIG. 1, moves the cutting edges of all thecircumferential lands toward one another and movement to the right movesthe cutting edges away from one another. Similarly, relative rotationalphase movement in one direction moves all of the cutting edges of theaxial land portions together and phase rotation in the oppositedirection moves them away from one another.

To prevent crushing and provide a clean cut of the web in the areaswhere the cutting edges shift from one side of the land to the other,coacting crossover sections 94 and 96 are formed in each blade at thepoints of transition which have very narrow land sections 98 and 100,which in registration, preferably cross generally at right angles toeach other. This narrow section is formed by relieving each landopposite its cutting edge which forms a very narrow outer face portion98 and 100. This relief both prevents the web material from beingcrushed between the lands where they cross and provides a clearance orspace to receive the severed portion of the web when it is cut in acrossover area. Usually, the width of the outer faces 98 and 100 of eachland crossover section is in the range of about 0.0002 to 0.008 of aninch, desirably about 0.0005 to 0.005 of an inch, and preferably about0.001 to 0.002 of an inch. The longitudinal length of this narrow outerface is usually in the range of about 0.010 to 0.150 of an inch,desirably about 0.015 to 0.080 of an inch, frequently about 0.015 to0.040 of an inch, and preferably about 0.015 to 0.025 of an inch. Thelayout and arrangement of the land portions, cutting edges, andcrossover sections of the coacting blades 26 and 28 of the die cylindersis disclosed and described in greater detail in U.S. Pat. No. 4,608,895issued on Sep. 2, 1986, the disclosure of which is incorporated hereinby reference and hence will not be described in further detail.

Blade Lands

In accordance with this invention to provide improved cutting blades andcutting performance, the blade lands have a specific geometry andconstruction. As shown in FIGS. 1 & 2, the axially extending landportion of each blade has an arcuate outer face 102 and a depending sidewall 104 adjacent its cutting edge which, as shown in FIG. 12, isessentially perpendicular or at a right angle to the chord 106 of thearcuate outer face 102. Preferably, the other land sidewall 108 issubstantially parallel to the sidewall 104. The intersection of thesidewall 104 and the outer face 102 forms the cutting edge 72 of thisblade land portion and preferably, but not necessarily, the other edgeis relieved by a chamfer or bevel 110 to facilitate ejection of the cutblank. However, as shown in FIG. 3, in some applications it may beacceptable to omit the chamfer so that the outer face 102 and sidewall108 intersect to define an edge 112. Preferably, as shown in FIG. 12,the chord is also essentially perpendicular to a radius 113 of thecylinder passing through its axis of rotation 52 or 54 and bisecting thechord 106 or being equally spaced between the parallel sidewalls 104 and108.

Similarly, as shown in FIG. 4, the circumferentially extending landportion of each blade has an outer face 114 which in cross section is astraight line, and a depending sidewall 116 essentially perpendicular tothe outer face 114. Since in cross section outer face 114 is a straightline it can be considered to either have no chord or its outer face andchord are one and the same thing. Preferably, the other sidewall 118 issubstantially parallel to the sidewall 116. The intersection of thesidewall 116 and the outer face 114 forms the cutting edge of the bladeand preferably the other edge has a chamfer or bevel 120 providingrelief which facilitates ejection of the cut blank. In some applicationsthe relief may be omitted and the sidewall and outer face will form asubstantially right angular edge.

The outer faces 102 & 114 of all of the lands are all concentric withthe axis 52 or 54 of their associated cylinder 20 or 22, are alldisposed essentially the same radial distance from its axis of rotationand are preferably all formed at substantially the same time bymachining a cylindrical peripheral surface on the cylinder coincidentwith its axis.

This specific construction and arrangement of the lands of the cuttingblades has the substantial advantages of significantly increasing theuseful life of the die cylinders, substantially reducing the cuttingforce required to sever or cut a web of material and thereby increasingthe useful life of the die cylinders and reducing the power required torotate the die cylinders, substantially decreasing the likelihood that acut blank will become caught or hung up in the die cylinder, providingblades which can be easily, quickly and inexpensively sharpened bysimply grinding and slightly reducing the radius of the outer faces 102& 114 of the lands, can be resharpened essentially without changing thesize and configuration of the blanks cut by the dies cylinders,eliminates most, if not all, manual or hand grinding and machining toresharpen the blades, enables the cutting blades to be formed byutilizing conventional cutting tools and grinding techniques andeliminates the necessity of electrical discharge machining of the bladeson the die cylinders.

Preferably, but not necessarily, each die may have a pair of spacedapart cylindrical bearer surfaces 122 which, when they bear on thecomplementary die cylinder, prevent the cutting blades from radiallyoverlapping and interfering with each other. The radius of thecylindrical bearer surfaces 122 must be no less than the radius of theouter faces 102 & 114 of the cutting blades and preferably are formedsimultaneously with the outer faces and may have the same or a slightlylarger radius.

Ejector Lands

In accordance with another feature of this invention, and as shown inFIGS. 1 and 4, removal of a cut blank 30 from the nip 34 of the diecylinders may be facilitated by the ejector lands 36, 38, 40 & 42 whichare located within the perimeter of the cutting blade of theirassociated die cylinder. As shown in FIG. 4, each ejector land isassociated with a pair of coacting blade lands and extends generallyparallel to and is disposed inwardly thereof. In operation, the landsflex or bend the somewhat resilient blank 30 adjacent its edges as it isbeing cut so that as it emerges from the nip of the die cylinders ittends to spring back to its unflexed generally flat condition therebydisengaging from the sidewall 104 or 116 of the associated cutting landwith which the cut edge of the blank is radially overlapped in the nip.With respect to its associated pair of cutting lands, the ejector landis disposed on the same die cylinder as the cutting land with which thecut edge of the blank radially overlaps in the nip and is spacedtherefrom so that the other cutting land on which the blank bears isdisposed between them. For example, in FIG. 4, the ejector land 36associated with cutting lands 58 & 74 is on cylinder 20 and the ejectorland 38 associated with cutting lands 66 & 82 is on the cylinder 22.

In cross section, the outer face 124 of the axially extending ejectorlands 40 & 42 is preferably arcuate and in cross section the outer face126 of the circumferentially extending lands 36 & 38 is preferably astraight line. Preferably, the outer faces of all of the ejector landshave the same radius as the outer faces of the cutting blade lands ofthe same cylinder on which the ejector lands are disposed and may beformed at the same time by machining a cylindrical surface coincidentwith the axis of the die cylinder.

Typically, in cross section the cutting blade and ejector lands have aradial height of about 0.010 to 0.125 of an inch, and desirably about0.020 to 0.090 of an inch, and preferably about 0.060 to 0.080 of aninch, and a transverse width of about 0.040 to 0.150 of an inch,desirably 0.075 to 0.140 of an inch, and preferably 0.100 to 0.125 of aninch.

Of course, if desired, the ejector lands may be interrupted ordiscontinuous and in their plan view have other shapes such as arcuate,circular, oval, square, a series of discrete segments, etc. Similarily,the shape of the sidewalls of the ejector lands is not critical and incross section they may be other than straight, such as arcuate.

As shown in FIG. 5, when after use the cutting blades are resharpened,such as by grinding the outer faces of the lands of the blades and theejectors, even though the extent of their radial projection is reduced,they still maintain the proper relationship and registration for bothcutting the blank and flexing or bending it to facilitate ejection ofthe cut blank from the the die cylinders. Indeed, even when sharpenedthe ejector lands flex or bend the cut blank to the same extent as theydid before resharpening so long as in use the same radial gap orclearance is maintained between the cutting blades of the die cylinders.As shown in FIG. 5, resharpening of the cutting blades makes no changein the axial or lateral width of the cut blank and virtually no changein the circumferential or longitudinal length of the cut blank becausethe sidewall 104 or 116 of each land adjacent its cutting edge isessentially perpendicular to the outer face 102 or 114 of the land orits chord 106.

Using the Die Cylinders

To use the rotary dies 20 & 22, they may be journalled for rotation insuperimposed relation by a die stand having for each die cylinder a pairof spaced apart arbors with opposed spindles having noses complementaryto and received in the recesses 44 in the opposed ends 46 & 48 of eachcylinder. Typically, the spindles are driven in timed relationshipthrough a gear train by a suitable prime mover, such as an electricmotor. Usually, the gear train includes a mechanism permitting theangular or rotary phase relationship of the die cylinders to be adjustedfor registration of the coacting and generally axially extending landportions of the cutting blades. The arbor assembly also contains asuitable mechanism for relatively axially shifting one of the pair ofdie cylinders to provide proper registration for the coacting cuttingedges of the generally circumferentially extending land portions of thecutting blades. Since a suitable die stand with arbors for journallingand driving the die cylinders and mechanism for adjusting their axialand rotary phase relationship is disclosed and claimed in U.S. patentapplication Ser. No. 08/002,660 filed on Jan. 11, 1993, the disclosureof which is incorporated herein by reference, it will be not bedescribed in further detail.

In use, the pair of die cylinders 20 & 22 are corotated in oppositedirections of rotation with the same peripheral surface speed of theouter faces of their cutting blades with the web 32 of material passingthrough their nip 34 at the same lineal surface speed. In the nip theblade lands coact to cut a blank 30 from the web. The ejector lands 36,38, 40 & 42 greatly reduce the likelihood of the cut blank becomingcaught or hung up in the blades. It is believed the ejector lands reducethe tendency of the cut blank to hang up because (1) they bend or flexthe blank which tends to foreshorten both its axial or lateral width andits longitudinal or circumferential length thereby providing increasedclearance between its edges and the cutting blades, and (2) due to theresiliency of the cut blank as it emerges from the nip of the die itsleading edge tends to move radially away from and out of radialoverlapping engagement with the immediately adjacent cutting blade land60. Furthermore, the right angular sidewall 104, 116 of the cuttingblades decrease the tendency of the edge of the blank to hang up thereoncompared to the inclined or raked sidewalls of prior art cutting blades.Regardless of any theoretical explanation, the ejector landssignificantly reduce the tendency or likelihood of the cut blanks tohang up or jam in the die cylinders.

Method of Making the Die Cylinders

In accordance with this invention, the die cylinders can be made bymachining with conventional cutting tools and grinding a workpiece ofunhardened tool steel to completely form the lands of the ejector andcutting blades and thereafter hardened by heat treating the cuttingblades for increased useful life without hardening the core or body ofthe cylinder. This avoids distortion of the cutting blades which wouldadversely affect their geometry and performance. As shown in FIG. 6, agenerally cylindrical workpiece 130 for making a die cylinder 20 or 22can be cut off from a piece of round bar stock 132 of tool steel by arotating milling cutter 134 received in a drive spindle 136 of asuitable machine tool. The milling cutter also machines one end face ofthe workpiece and the other end face can be simultaneously machined by arotating end mill cutting tool 138 received in a drive spindle 140 toprovide the workpiece 130 with end faces 46 & 48 substantiallyperpendicular to its longitudinal axis and of the desired length of thedie cylinder.

As shown in FIG. 7, the recesses 44 are machined in the workpiece withthe frusto conical locator surfaces 50 on a common axis, preferablysimultaneously, by two opposed rotating boring tools 142 in drivespindles 144 of a suitable machine tool. Thereafter, as shown in FIG. 8,the keyway 56 can be machined in one or both recesses of the workpieceby rotating milling tools 146 received in drive spindles 148 of amachine tool. If desired, all of the machining operations of FIGS. 6, 7and 8 can be formed with the same machine tool, such as a computerizednumerical control (CNC) machining center having drive spindles movablealong three orthogonal axes.

As shown in FIG. 9, to form the outer faces 102 & 114 of the cuttinglands (and preferably the outer faces 124 & 126 of the ejector lands),the workpiece 130 is accurately located and rotated in a machine tool150 by arbors 152 with spindles 154 having complementary noses 156engaging the recesses 44 in the ends of the workpiece. A cylindricalsurface 158 concentric with the common axis 52 or 54 of the recesses ismachined on the workpiece by a suitable tool, such as an end mill 160,rotated and axially reciprocated by a drive spindle 162 of the machinetool while the workpiece 130 is rotated by the machine tool.

As shown in FIG. 10, the lands of the cutting blades and ejectors areformed in the workpiece by machining away portions of the periphery ofthe workpiece. Preferably, peripheral portions are machined away inrough and finish cuts by a milling tool 164 rotated and moved alongvarious axes by the spindle 162 in coordination with angular or arcuatemovement of the workpiece 130 about its axis by the arbor spindles 154.Preferably, the coordinated movement of the spindle 162 and theworkpiece 130 is performed by a computerized numerical control machinestool 150 having at least three orthogonal axes of movement of thespindles relative to the workpiece and one arcuate or rotary axis ofmovement of the workpiece relative to the spindle. Preferably, thismachining is performed on a so-called five axis or six axis computerizednumerical control machine tool 150.

As shown in FIGS. 1 & 12, when machining the sidewall 104 (andpreferably also sidewall 108) of a generally axially extending cuttingland (60, 68, 76 or 84) the axis 166 of rotation of the cutting tool 164is oriented so that it is essentially perpendicular to the chord 106 ofthe arcuate outer face 102 and hence is not parallel with and is skewedto a radius 168 of the workpiece which intersects the plane of the sideface of the blade being machined by the cutting tool. With a CNC machinetool it is feasible and practical to machine the side faces of all ofthe land portions of the cutting blades so they are essentiallyperpendicular to the cord of the corresponding outer face regardless ofwhether such land portion of the cutting blade extends axially,circumferentially or obliquely on the cylindrical workpiece, and hencethe finished die cylinder. After machining the sidewalls of the bladelands, the bevelled edge 110 can be machined with an end milling toolreceived in the spindle 162 of the CNC machine tool.

In a similar manner, the sidewalls of the ejector lands 36, 38, 40 & 42can be machined by the rotating milling tool 164 in the drive spindle162 of the CNC machine tool. The sidewall 170 of each bearer 122 canalso be machined with the milling tool 164 by the CNC machine tool 150.

As will be appreciated, after machining away peripheral portions of theworkpiece and machining the sidewalls of the blade and ejector landstheir outer faces are the remaining portions of the cylindrical surface158 previously machined on the workpiece 130. However, if desired, theouter faces of the blade and ejector lands could be machined after,rather than before, their sidewalls by the CNC machine tool 150,although it is preferable to machine them beforehand.

After machining is completed, as shown in FIG. 13, the cutting bladelands can be hardened by heating them to an elevated temperaturetypically about 1000° F. to 1200° F. with a laser 172 and quenching themwithout substantially hardening the core or body of the workpiece 130and hence without distorting it by heat treating it. The emitter 174 ofthe laser 172 can be received in the spindle 162 of the CNC machine toolfor orienting and manipulating it to direct its beam 176 of coherentelectromagnetic radiation onto each cutting blade land of the workpiece130 while it is received and located by its recesses 44 on the arbors152 of the machine tool and arcuately moved by them as needed to directthe laser beam onto the cutting lands. Preferably, the heated lands arequenched to cool and harden them by air cooling or if needed to controlthe rate at which they are cooled by contacting the blades with asuitable quenching liquid, such as by spraying, pouring or directing astream of the liquid onto the blades or immersing the blades in theliquid.

When the cutting blades of the die cylinder become dull from use, theycan be resharpened such as by grinding the outer faces of the cuttinglands while the workpiece 130 is located by its recesses 44 to produceouter faces of the cutting blade lands which are essentially concentricwith the axis of rotation of the workpiece.

This method of making the die cylinders has the substantial advantagesof utilizing conventional cutting tools and CNC machine tools, machiningthe workpiece before the cutting blades are hardened, producing highlyaccurate and precise die cylinders, eliminating the need for electricdischarge machining, and being relatively quick, easy, economical andrequiring significantly less capital investment to produce rotary dies.

What is claimed is:
 1. Rotary dies which define a nip therebetween forcutting a web of material passing through the nip, said rotary diescomprising: a pair of coacting die cylinders of metal constructed andarranged to be journalled for co-rotation, at least one pair of coactingelongate severing blades with one blade of each pair disposed on one ofsaid die cylinders, each severing blade comprising an elongate landprojecting generally radially outwardly from and integral with itsassociated die cylinder, each said elongate land having an outer faceand spaced apart and generally depending side faces, said outer facehaving a width of at least 0.040 of an inch, in cross section at leastone of said side faces of each land being essentially perpendicular tosaid outer face if said outer face is linear or to a chord of said outerface if said outer face is arcuate, said one side face and said outerface of each land intersecting to define a cutting edge on the landthereof, said coacting severing blades of each pair being constructed,arranged and positioned on their respective die cylinders so that duringco-rotation of said pair of die cylinders the cutting edges of saidcoacting severing blades of each pair which are immediately adjacent cutthe web therebetween along a predetermined line of severance while theother edges of the coacting severing blades are on generally oppositesides of the line of severance, the line of severance subtending morethan one quadrant, and at least one pair of coacting crossover sectionseach in one blade of said pair of severing blades, each said crossoversection having a narrow segment of its outer face with a maximum widthsubstantially less than the maximum width of adjacent portions of theouter face of its associated blade, said narrow segment lyingimmediately adjacent the line of severance and extending at least to thepoint where the cutting action of said coacting severing bladestransfers over from one cutting edge to the other cutting edge of saidlands of said severing blades, whereby the pair of die cylinders may beshifted generally axially with respect to each other and shifted inrotational phase relationship with respect to each other so that anappropriate relationship between all of the severing blades thereof ismaintained for cutting the web along the predetermined line ofseverance.
 2. The dies of claim 1 wherein the maximum width of the outerface of each of said lands is in the range of about 0.04 to 0.15 of aninch.
 3. The dies of claim 1 wherein the maximum width of the outer faceof each of said lands is in the range of about 0.100 to 0.125 of aninch.
 4. The dies of claim 1 wherein the outer face of each of saidlands is disposed generally radially outwardly of the main body of itsassociated die cylinder in the range of about 0.010 to 0.125 of an inch.5. The dies of claim 1 wherein an edge of each land spaced from saidcutting edge has a chamfer thereon.
 6. The dies of claim 1 which alsocomprises an elongate and rigid ejector land associated with said onepair of coacting severing blade lands and received on and integral withone of the die cylinders within the perimeter of the line of severanceand extending generally parallel to a portion of said pair of coactingsevering blade lands so that in cross section one of said blade lands ispositioned between the other of said blade lands and said ejector landso that as a portion of material is cut from the web its opposed sidefaces bear on and are flexed by the cooperation of said ejector land andsaid one blade land received between said ejector land and said otherblade land.
 7. The dies of claim 6 wherein said ejector land has anouter face radially co-terminous with the outer face of said associatedblade land integral with its associated die cylinder.
 8. The dies ofclaim 7 wherein in cross section the outer face of said ejector land hasa width in the range of about 0.04 to 0.15 of an inch.
 9. The rotarydies of claim 1 wherein each die cylinder has a pair of recesses in itsopposed ends for removably receiving spindles for journaling said diecylinders for co-rotation, each recess having a frusto conical locatorsurface therein for complimentary mating engagement with one of thespindles to accurately locate the one spindle on its respective diecylinder, and the frusto conical locator surfaces of each die cylinderbeing coaxial with each other and concentric with the axis of rotationof the die cylinder.